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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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MILES AND GBINNELL GLACIERS                           435
terminus and the river, though without suggestion whether this moraine was underlain by ice or not. Hayes does not mention this glacier in the text.
Both Spencer's and Moffit's photographs show clearly that the stagnant outer portion had almost exactly the same relationships in 1900 and 1907 that they had in 1910. In 1906 and ensuing years incidental observations of Grinnell Glacier were made by the railway engineers, who named this ice tongue. In 1909 two important photographs of Grinnell Glacier were taken by E. A. Hegg of Cordova.
In 1909 we saw Grinnell Glacier in passing, but gave no time to its study. In August, 1910, and in June, 1911, four days were devoted by the junior author to its examination.
Cascading Ice Tongue. The snowfields of Grinnell Glacier are not visible from its lower portion, but the abrupt topography suggests that they occupy a series of deep glacial cirques. There are at least three important tributaries. The clear ice terminates in two minor lobes. Most of the clear ice portion of the glacier that we have seen, photographed, or mapped, is cascading down a moderate slope and is severely crevassed. The highest point on the glacier whose elevation we determined is 2000 feet above sea level or 1500 feet above the terminus of the clear ice, the slope here being at the rate of nearly 2000 feet to the mile. Higher portions of the ice tongue near the snowfield have even steeper slopes, but in an intermediate portion above the 2000 foot contour the grade of the glacier flattens somewhat. This cascading terminus is interrupted as the result of a discordance of over 2000 feet between the grades of Grinnell and Copper River valleys. The glacier still occupies its hanging valley and expands slightly in the moraine-covered terminus at its base. The thinness of the ice on the hanging valley lip is shown by the bare rock slope between the northern and southern lobes.
The mountain valley occupied by the glacier is exceptionally steep-sided, and also those of two detached tributary glaciers on the northern wall. These hanging glaciers now terminate 2800 and 3200 feet above sea level and their slopes are over 2800 feet to the mile. Just east of these hanging glaciers the northern valley wall slopes at the rate of over 6300 feet to the mile but the southern wall is not so steep.
Stagnant Southern Lobe. The southern lobe of the clear ice grades eastward through a zone of barren, thin, ablation moraine to a zone of thick ablation moraine, which mantles the ice so completely that it supports vegetation which entirely covers the surface. The end of the lobe does not look at all like a glacier and would not be known to be underlain by ice were it not for occasional slumping of the surface in the forested zone, and the exposed northwest-facing slope of black ice, studded with bowlders, in the zone of barren moraine.
Forested Hill at Terminus. Grinnell Glacier terminates in a forested hill (Fig. 67), which we believe to be wholly composed of ice. This belief is based upon the fact that here and there in this outer portion are areas of slumping where trees are being overturned. In several places, a whole steep slope has lost all its vegetation by the slumping attendant upon melting of the ice beneath, The cliff facing the edge of the interior flat at a number of points shows dark ice, filled with bowlders. At one locality near the northern edge the thickness of the ice revealed is 30 to 35 feet, above which are about 2 or 3 feet of morainic material in which shrubs are growing (PI. GLXVII, B). Throughout the terminal hill of moraine-covered ice there are a great many areas of recent slumping and of emergence of water. The shrubs growing on the high outer